Frequency modulation



NQ'W0 1948. Q Q Q LUCK FREQUENCY MoDULATIoN Filedl Feb. 17, 1945 2Fsneets-'sheet 2 N m T m M 0 M ouv-Par NOT 019059 FREQUENCY Mao U4 nrEaOa TPU 7' f1 TTORNEK Patented Nov. 30, 1948 David G. C. Luck,Hightstown, ISL-J., assgnor to Radio Corporation of America, acorporatlon of Delaware Application vFebruary 17, 1943, Serial No.476,145

n 11 Claims. l

This application discloses a new and improved means for producingfrequencymodulationof a carrier of stable frequency.

In 'my improved vsystem .Ifmodulate the wave length ofoscillationsfgen'erated by an oscillation generator of the type in whichthe frequency of oscillations produced is controlled by means of amagnetostrictive body. To do lso I supply a v polarizing force to the`magnetostrictive element which varies in accordance with signalvariations to thereby vary the period of Vibration of the said elementand as aconsequence the frequency of the oscillations generated.

The signals may be of any type providingtheir highest frequencydoes notexceed'the frequency of the generated carrier in turn limited byseifresonan'ces of-'magnetizing windings on the magneto'strictive body.

In describing the invention reference is made to frequency modulation ofthe oscillations. The modulations may be asto freduency-or-phase orvariations of :either or both depending on the treatment 'of themodulation before it is used to modulate the generated oscillations. Theterm instantaneous frequency modulation is used kto cover these varioustypes of modulation.

Various forms of my invention are illustrated in the drawings whereinFigure 1 is a `simplified showing of a magnetostriction generator withconnections for varying the `frequency of the generated wave. Figures 2,3 and 4 are more complete showings of the arrangement of Figure 1 andvmodifications thereof. I

Ifl an element I having magnetostrictive properties-(polarizedpermanently bya source I2 connected with windings Ill)` is vibratedmechanically it will feed voltage to leads I6 connected with windings I8also associated with the magnetostrictivemember IG. These voltages willbe of affrequency determined by the elasticity and the dimensions of theelement I0. If the generated oscillations are fed into a negativeconductance Aor resistance device 20 sustained oscillations aregenerated in' the device'20 .and winding I8 due to the' fact that thenegative resistance device 2U feeds power back to the winding I8 todrive lthe element Ill at its natural frequency.

By properly arranging 'the mechanical resonator systema very stableoscillation generator is obtained.

Thevmagnetic field strength inuences the frequency at which themagnetostrictive oscillator operates and I make'use of thispropertytofmodulate the frequency of the generated oscillations.

-I vary the voltage in the polarizing winding Ill :increase thedeviationv the desired extent. If-the oscillator was `of 4an unstabletype suchmultiplication could not .be used.

The negative conductance device may, as illustrated in Figure.2,comprisea tube 30 having an anodel-32 voperating at less potential than itsscreen grid-34 to obtain the dynatron or negative resistance effect.vThe plate direct current circuit is completed tosource II by the windingI8. YA .tuningcondenser I5 shunts the winding I8 and the plate impedanceof the negative resistancevdriver tube .30. vThis `tuning condenser isnecessary for efficient loading of the negative resistance driver tubey30.

vThe winding ISis also included in a direct current polarizing circuitincluding the choke RFC, the` secondary winding of modulationtransformer 41, adjustable resistorZd .and source II. lCondenser-36.outside (with respect to the generating circuit) Athe radio choke RFCvby-passes residual radio frequency around the modulator including thesecondary winding of transformerll'l.

The modulator tube 40 has its input excited by modulation currents andits anode connected through -.the primary winding of transformer il andsource II to Aits cathode. The source II is shunted by modulationfrequency by-pass condenser ffi3. Asstated/above-the secondary windingoftransformer 41 is in the polarizing circuit of winding r`I-Yandmcdulation frequency by-pass condenser 45 passes ythe modulationaround the polarizing source II. `An `impedance matching VtransformerVis usedat fito properly load the modulator tube 40.

The egenerated and timing modulated carrier isfed 4lay-couplingcondenser 546 and bias impedance 48 -to-an amplierstage tube 50 theanode of which supplies the output toadditional stages such as frequencydividers or heterodyne frequency changers to lower its frequency or tofrequency multipliers `or .heterodyne yfrequency changersto increase itsfrequency.

modulated by tube 40 to vary the iield in accord-` ance with themodulation. Negative conductance tube 30 and winding I8 operate tomaintain the element I in oscillation at its natural frequency butmodiiied some by the field variations. The modulation source isprevented from unduly loading the bar by the choke RFC and the output isso arranged so that it does not load the system. The dimensions ofwinding I8 are suitable to the d pling coil I9 as shown, but they mayinstead be derived from an impedance inserted in the lead to anelectrode in tube 30, so long as this impedance can .be prevented fromspoiling the operation of the negative transconductance.

In the prior figures an oscillation generator of the negative resistanceor dynatron type has been rshown and a single winding I8is connectedwith this negative resistance'tube 38. It will be understood, however,that I may make use of an oscillation generator of the regenerative typein which case there is a grid winding on the element IU V as well as aplate winding I8. The generated voltage polarity is such with respect tothe windings and element II! that the grid winding is excited by changein the ux caused by physical disturbance of the element I0 and thisresults in Vari- Y able current in the plate winding to furtherstimgenerated frequency and` for producing the polar'- izing ield andvarying the same in accordance with the control potentials. Thegenerated oscillations are modulated as to timing in accordance with thecurrent fed to the input of tube 4U.

' In the modification of Figure 3 a separate winding 5U is provided formodulation of the polarization of the magnetostrictive element I0 andthe direct current for the tube' 4B is permitted to iiow in thiswinding. The direct plate current of tube 30 Ialso flows in winding I8.`An advantage 0btained by use of the separate windings is that each coilmay be constructed and arranged for optimum operation. The highfrequency coils should be concentrated on regions of maximum oscillatingstrain of the magnetostrictive bar I0 and should be magnetically snug onthe bar (but not touching mechanically). The low frequency coilvgeometry is less important.

In Figure 3 the battery I2 and winding I4 polarize rod I0 to a pointgiving best'compromise between modulation capability and operatingefficiency, the chokes preventing this circuit-from loading down otherscoupled to it. The modulating tube 4D and winding 50 swingthe polarizingiield in accordance with the output of the modulating source. ductancedevice (dynatron or transitron) 3l] enable energy from the plate batteryto-maintain bar IU in oscillation at its own natural resonant frequency,by virtue of the coupling provided by the magnetostrictive propertiesofthe bar. The output coil I9 permits utilization'of flux variations inthe bar, but the utilization circuit must not load the bar markedly oroscillation may stop. When flux change due to changing strain in themagnetostrictive bar I8 induces voltage in coil' I8, the function ofdevice 30 is to produce current in coil i 8 tending to aid the Ioriginalux change. The non-linearity of device 30 limits swings so produced,permitting oscillation.

In the modification of Figure 4 the winding I3 is shunted by a tuningcondenser 'I0 which with the winding I8 provides a circuit tunedsubstantially to the mean frequency of operation of the generator. Theoutput is supplied by connections across this tuned circuit and theoutput circuits are such that they do not load the generator and preventoperation thereof due to damping.

vModulation is supplied across a modulation reactor 12 in series withwinding I4 and source I2.

The operation of this modication is essentially as describedhereinbefore. v

In the arrangements of Figures 1, 2, 3, and 4 timing modulated voltagesfor external use are derived inductively from the rod, either directlythrough winding I8 or through a separate cou- Coil I8 andnegative'transcon ulate the element to alter its dimensions. Thisdistortion acts through' the element and flux to further excite the gridand thus to develop sustained oscillations.

I claim:

l. In a system of the class described, an element havingmagnetostrictive properties, a direct current polarizing circuittherefor, a tube generator having electrodes coupled to a winding themagnetic `field of which includes said element, the arrangement beingsuch that said element vibrates at a frequency determined in part by thepolarizing direct current intensity and vibration of said elementapplies voltages to the said tube electrodes and the tube 'feeds Vpowerback to said winding to develop in the arrangement oscillations ofsubstantially fixed frequency, and a source of modulating currentcoupled to a winding the magnetic field of which is cut by said elementfor varying the polarization thereof and correspondingly varying thefrequency of the oscillations generated.

2. In a modulation system, an element having magnetostrictiveproperties, a tube having electrodes, a source of modulation currents, acircuit coupled to said source so that modulation current iiows in saidcircuit, a winding for producing a magnetic iield cut by said elementfor polarizing said element, a source of direct current, connectionsincluding said winding, said'first mentioned circuit and said source ofdirect current in series, and other connections coupling said winding toelectrodes of said tube, whereby frequency modulated oscillations areproduced in said system.

3. In a modulation system, an element having magnetostrictiveproperties,J a direct current polarizing circuit therefor including amagnetic eld producing winding and a source of direct current in seriestherewith, a modulation potential impedance in series in said circuit,means for applying modulating potentials to said impedance, an electrondischarge device having output electrodes, a second winding the magneticeld of which is cut by said element, means coupling said second windingwith the output electrodes of said device, and an output circuit coupledwith said last mentioned winding.

4. In a system as described, a magnetostrictive vibrator, a iield'winding in a circuit including a source of current for' producing amagnetic iield wherein said vibrator is located, an oscillationgenerator circuit the frequency of operation of which is controlled by`said magnetostrictive vibrator located in said magnetic field producedby current in said field winding, a variable impedance eiectively in thepath of said current, and a source of control potentials associated withsaid impedance for varying the strength of the current in said fieldWinding in accordance With said control potentials and correspondinglyvarying the instantaneous frequency of the oscillations generated.

5. In a system as described, an oscillation generator comprising a tubehaving electrodes in an oscillation generating circuit, amagnetostrictive element in a polarizing field, at least one WindingAhaving a magnetic eld cut by said element,-

irneans coupling said Winding to the tube elec- `trodes to include saidWinding in the oscillation generating circuit to determine its frequencyof operation, means for producing said polarizing field including asource of direct current, and means in series with said source forvarying the strength of said polarizing eld in accordance with signalsto correspondingly vary the frequency of operation of said generator.

6. In a system as described, a resonant magnetostrictive element, afield winding, a source of direct current, connections including saideld Winding and direct current source in a circuit for producing apolarizing field wherein said element is located, an oscillationgenerator the irequency of operation oi which is controlled by saidresonant magnetostrictive element, a variable impedance in said directcurrent circuit, and a source of signal currents associated with saidimpedance for varying the current in said direct current -circuit andthe polarization of said element in accordance With said signal currentsto correspondingly vary the frequency of operation of said generator.

'7. In a system of the nature described, an oscillation generatorcircuit the frequency of operation of which is controlled by a resonantmagnetostrictive element in a uni-directional magnetic field formed by awinding on said element, said Winding being included in said firstcircuit and connected to a source of direct current and an impedance, onwhich signal voltages are applied, connected to said direct currentsource t-o vary the current flow in said Winding and modulate thestrength of said eld in ac cordance with signals.

8. In a system of the nature described, a magnetostrictive elementincluded in the magnet-ic field yof a rst Winding in a circuit with anegative conductance, a second winding connected to a source of directcurrent for pr-oducing a magnetic field in which said element islocated, an impedance in series with said last Winding, and means forimpressing modulating potentials on said impedance for modulating thedirect current in said last Winding to correspondingly vary said fieldin accordance with modulating potentials.

9. In a system of the nature described, an oscillation generator circuitof controllable irequency comprising a tube having electrodes, anelement having magnetostrictive properties located within the magneticeld of a first winding coupled to electrodes of said tube t-o determinethe frequency of operation of said generator circuit, a magnetic eldproducing winding on said element, a source of direct current -connectedto said eld winding for producing a magnetic eld in which the element islocated and an impedance connected with said eld Winding for modulatingthe direct current therethrough in accordance With modulatingpotentials.

10. In a system of the nature described, a tube having electrodes, anelement having magnetostrictive properties, at least one windingmagnetically coupled to said element an-d electrically coupled to saidtube electrodes, a magnetic field producing Winding arranged to producea magnetic field cut iby said element, a source of direct currentconnected to said eld producing Winding, a third Winding whose magneticfield is cut by said element, a source of potentials representingsignals, `and connections from said source of potentials to said thirdWinding for causing current characteristic of said signals to flow insaid third winding.

1l.. In a system of the nature described, an element havingmagnetostrictive properties located in the magnetic iield of a iirstWinding, means connecting said first winding in circuit with a negativeresistan-ce, a second Winding for producing a magnetic eld cut `by saidelement, a source of direct current connected to said Second winding, athird Winding for producing a magnetic field cut by said element, asource of potentials representing signals, and connections from saidlast source to said third Winding for causing current characteristic ofsaid signals to ow in said third winding.

DAVID G. C. LUCK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,750,124 Pierce Mar. 11, 19301,841,459 Taylor Jan. 19, 1932 1,937,333 Dome Nov. 28, 1933 2,000,025Ide May 7, 1935 2,139,238 Linder Dec. 6, 1938 2,174,701 Koch Oct. 3,1939 FOREIGN PATENTS Number Country Date 530,059 Germany July 20, 1931OTHER REFERENCES Pro. Amer. Adad. -of Arts .and Sciences, April 1928,vol. 53, No. 2, pages 49-66, particularly pages 59 and 60. (Copy inLibrary.)

